Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
Voir sur la carte

Danger d’avalanche

Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
Open full map
Périmé — ce bulletin a expiré 10 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Considerable avalanche danger exists today due to wind slabs and persistent slabs.  Wind slabs will exist on NW-N-NE-E-SE-S aspects in near treeline terrain and above treeline terrain.  Persistent slabs will exist on North aspects where previous old snow existed from late October and early November.  Dangerous avalanche conditions exist.  Careful snowpack evaluation, cautious route finding, and conservative decision making is essential.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1

    Winds overnight during most of the snowfall were from the SW in the moderate to strong range with some locations gusting much higher.  Wind slabs could have developed on NW-N-NE-E-SE aspects overnight.  As winds shift towards the W and then eventually to the NW throughout the day, wind slabs will continue to grow and may develop on SE-S aspects near and above treeline as well.  Most wind slab problems today will be on slopes 35 degrees and steeper.  Slopes with previous snow with some or all anchors covered up will be the most susceptible to wind slab formation.

    Look for areas of blowing snow, cornice formation, and wind pillows.  Any cracking around skis in wind loaded terrain will be an indication that wind slabs have or are developing.  Even a small avalanche has great consequences with our early season snowpack.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2

    Snow that fell in late October and early November has become faceted and weak.  These conditions exist on North aspects along the Sierra Crest north of Tahoe City above 8300' and in the Mt. Rose area above 9000'.  Snowpack tests in the Castle Peak area and the Mt. Rose area indicate that this persistent weak layer could propagate if triggered.  With the load of additional snow last night, these persistent slabs may become easier to trigger.  This problem could exist on slopes 30 degrees and steeper.

    These persistent slabs exist in exactly the same area with the most snow for recreation.  Persistent slabs can be remotely triggered, do not give reliable information with informal observations, and existing tracks do not indicate stability.  Digging in the snow may be required to see if this problem exists in your area on your specific slope.  Avoiding North aspects above 30 degrees is another strategy to deal with this persistent weak layer. 

Avalanche Discussion

Yesterday's observations on Tamarack Peak indicated that faceting has continued within the old snow from late October/early November.  Snowpack tests were mixed at many locations throughout the day.  The weak faceted layer was observed at all data gathering areas on North aspects above 9300' with more advanced faceting occurring above 9500'.  There was up to 1' of light unconsolidated snow on top of the weak layer.

Active wind transport was observed throughout the day with very little to no wind slab development seen.

The most usable snowpack within the forecast area exists along the northern portion of the Sierra Crest. Areas above 7,000' and north of Tahoe City have sufficient amounts of supportable snow for quality over snow travel (2 to 4 feet). Along the Sierra Crest south of Tahoe City, snowpack depths decrease dramatically, even at the highest elevations.  The Mount Rose area in the NE portion of the forecast area has decent snowcover (~2-3 feet) in areas that have held snow/ice since mid Oct. This is generally N aspects above 9,300'. Below 9,300' on N aspects or on all other aspects in the Mount Rose area, over snow travel is possible, but impact with rocks is likely with snow depths around 1-2 feet.

Due to the wide variances in snowcover between the northern and southern portions of the forecast area, this advisory is heavily biased towards the northern areas where the snowpack is more usable for over snow travel.

The avalanche center is still working on a limited number of observations so please submit observations through the "submit observations" buttons found throughout this website.

Régions couvertes